1. Field of the Invention
This invention generally relates to an image pick-up device and more particularly to an image pick-up device provided with image pick-up means to produce an electrical image pick-up signal and focus detecting or adjusting means to detect or adjust the focal point of an imaging lens system by virtue of the image pick-up means.
2. Description of the Prior Art
Focus detecting or adjusting devices, especially automatic focusing devices, have rapidly become popular, since being adopted for photographic film cameras. They are now in broad use for various cameras including 35 mm lens-shutter cameras, video cameras, 8 mm cameras, etc. Furthermore, the distance measuring method employed in these devices has proliferated into many different methods. These distance measuring methods, for example, include a method in which sound waves are emitted at an object to be photographed and the distance to the object is measured by finding a time difference between sound wave emission and return after they impinge on the object and bounce back. One method uses a detection circuit which produces a characteristic output when an image formed by an objective lens system becomes most sharp on a predetermined focal plane and another method is based on the principle of trigonometrical measurement. Of these methods, the trigonometrical distance measuring method is roughly divided into an active type in which a light, such as near infrared rays or the like, is projected on the object and a passive type in which a light emitted from the object is utilized.
The conventional technique, however, necessitates provision of an image pick-up element and a focus detection element even in cases where such focus detecting or adjusting devices are used for video cameras, TV cameras and the like. This has presented a problem in terms of cost, volume and weight.
A solution has been proposed which utilizes a portion of the image pick-up element for distance or focus detection. In that situation, however, the portion of the image pick-up element which is to be utilized for distance or focus detection is not used for the image pick-up intrinsic function. The image pick-up element thus cannot be used to its full extent for image pick-up. Another shortcoming of this prior art method is that the arrangement of the image pick-up element tends to cause difficulty in arranging an optical system for distance measurement or focal point detection. Furthermore, there is known another method in which a signal for distance measurement or focal point detection is obtained from a video signal. However, the latter method not only has the distance or focus detecting arrangement thereof limited to some specific application but also tends to complicate the circuit arrangement required.
An object of the present invention is to provide an image pick-up device in which an image pick-up element performs a combined function as a light receiving element for distance or focus detection by eliminating the above shortcoming of the arrangement of the prior art and in which the operation of video signal producing means and that of distance or focus detecting means are timely switched over from one to the other permitting reduction in the manufacturing cost, size and weight of the device.
Another object of the invention is to provide an image pick-up device which is not only capable of attaining the above object but is also capable of giving a highly realistic distance or focus detecting area for improved image pick-up, for example, by displaying an image of a projected light spot within an electronic viewfinder.